1. Field of the Invention
This invention relates to optical detection of defects in rotary cutting tools. It has particular advantage in association with rotary saws used to cut semiconductor wafers into segments.
2. Prior Art
Dicing saws are used to cut semiconductor wafers into individual dice. Each die is closely adjacent to its neighbors, and the wafer tends to be somewhat brittle. For this reason, it is important that the dicing saw have a blade which is appropriately sharp and having no defects.
The dicing saw is a rotary saw, and typically includes a diamond cutting blade. Because of the physical properties of the work (silicon wafers), defects in the dicing saw blade could cause chipping of the dice or otherwise damage the dice. It is possible that the damage caused by the defective saw could occur on numerous wafers.
A large percentage of the manufacturing costs of producing semiconductor wafers is in the fabrication of functional dice on the wafer. Therefore, it is important to avoid damaging these dice. If preliminary tests of the dice are made prior to cutting, a defect caused by cutting would go undetected until after assembly, resulting in packaging costs being incurred for defective parts. It is, therefore, important that defects in dicing saw blades be detected as soon as they occur.
If defects are automatically detected, then it is possible to shut down the dicing saw automatically, so that the operator may make a visual inspection prior to restarting the saw or deciding what attention the saw requires.